System for tunable workpiece biasing in a plasma reactor

ABSTRACT

Systems and methods for tunable workpiece biasing in a plasma reactor are provided herein. In some embodiments, a system includes: a plasma chamber that performs plasma processing on a workpiece, a first pulsed voltage source, coupled directly to a workpiece, a second pulsed voltage source, coupled capacitively to the workpiece, and a biasing controller comprising one or more processors, and memory, wherein the memory comprises a set of computer instructions that when executed by the one or more processors, independently controls the first pulsed voltage source and the second pulsed voltage source based on one or more parameters of the first pulsed voltage source and the second pulsed voltage source in order to tailor ion energy distribution of the flux of ions directed to the workpiece.

FIELD

Embodiments of the present disclosure generally relate to a system fortunable workpiece biasing in a plasma reactor.

BACKGROUND

Ion bombardment is often used as a source of activation energy forchemical and physical processes in etch and chemical vapor deposition(CVD) processes for processing a semiconductor workpiece, for example, awafer. Currently, wafer biasing technology uses radio frequency (RF)biasing techniques. These RF techniques generally use single frequencyRF biasing to accelerate ions to be implanted into a wafer, whichresults in a fairly well known distribution of ion energy across thewafer. However, the density of ions at a particular ion energy (eV) isalways distributed in well-known quantities, and the distribution is nottunable using RF biasing. Optimization of the etching process by carefulcontrol of the population of ions at a given ion energy is currently notpossible, and the effect of different ion energies on process results isnot known in detail.

Therefore, the inventors have provided a system that enables processingchambers to be tunable in order to tailor ion energy to independentlycontrol the maximum ion energy and the distribution of low and mediumion energies, or in other words, a system for tunable workpiece biasingin a plasma reactor.

SUMMARY

Systems and methods for tunable workpiece biasing in a plasma reactorare provided herein. In one embodiment, a system includes a plasmachamber that performs plasma processing on a workpiece, a first pulsedvoltage source, coupled directly to a workpiece, a second pulsed voltagesource, coupled capacitively to the workpiece, and a biasing controllercomprising one or more processors, and memory, wherein the memorycomprises a set of computer instructions that when executed by the oneor more processors, independently controls the first pulsed voltagesource and the second pulsed voltage source based on one or moreparameters of the first pulsed voltage source and the second pulsedvoltage source in order to tailor ion energy distribution of the flux ofions directed to the workpiece.

Another embodiment provides a method for tunable workpiece biasing in aplasma chamber. The method includes generating a high voltage by a firstpulsed voltage source and coupling the high voltage to a workpiece in aplasma chamber, generating one or more of low and medium voltages by asecond pulsed voltage source, coupling, capacitively, the one or more oflow and medium voltages to the workpiece and pulsing the high voltageand the one or more of low and medium voltages by a biasing controlleraccording to one or more parameters of the first pulsed voltage sourceand the second pulsed voltage source to tailor ion distribution in theworkpiece.

In yet another embodiment, a system for tunable workpiece biasingincludes a plasma chamber that performs plasma processing on aworkpiece, a plurality of first pulsed voltage sources, each of theplurality of first pulsed voltage sources individually coupled to one ormore pins electrically isolated from a base of the plasma chamber, theone or more pins being directly coupled to the workpiece in the plasmachamber, a second pulsed voltage source, coupled capacitively to theworkpiece and a biasing controller that independently controls the firstpulsed voltage source and the second pulsed voltage source based on oneor more parameters of the first pulsed voltage source and the secondpulsed voltage source in order to tailor ion energy distribution of theflux of ions directed to the workpiece.

Other and further embodiments of the present disclosure are describedbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure, briefly summarized above anddiscussed in greater detail below, can be understood by reference to theillustrative embodiments of the disclosure depicted in the appendeddrawings. However, the appended drawings illustrate only typicalembodiments of the disclosure and are therefore not to be consideredlimiting of scope, for the disclosure may admit to other equallyeffective embodiments.

FIG. 1 is a block diagram illustrating a system for tunable workpiecebiasing in accordance with exemplary embodiments of the presentdisclosure;

FIG. 2 is a block diagram of a biasing controller in accordance withexemplary embodiments of the present disclosure;

FIG. 3 is one example of an ion distribution curve generated by theapparatus of FIG. 1 in accordance with exemplary embodiments of thepresent disclosure;

FIG. 4 is a flow diagram representing a method of tailoring the iondistribution across a semiconductor workpiece in a plasma chamber inaccordance with exemplary embodiments of the present disclosure;

FIG. 5 illustrates a shaped pulse bias waveform emitted by the shapedbias waveform generator, and coupled to a plasma chamber in accordancewith exemplary embodiments of the present disclosure;

FIG. 6 illustrates a cyclic waveform emitted by the pulsed DC source inaccordance with exemplary embodiments of the present disclosure;

FIG. 7 is a block diagram of another embodiment of the system fortunable workpiece biasing in accordance with exemplary embodiments ofthe present disclosure; and

FIG. 8 is a block diagram of yet another embodiment of the system fortunable workpiece biasing in accordance with exemplary embodiments ofthe present disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The figures are not drawn to scale and may be simplifiedfor clarity. Elements and features of one embodiment may be beneficiallyincorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

Embodiments of a method and apparatus for tunable workpiece biasing in aplasma reactor are provided herein. In some embodiments, a system fortunable workpiece biasing in a plasma reactor includes a high voltagepulsed DC source (a first pulsed voltage source) coupled to a plasmareactor, a second pulsed voltage source that supplies low and mediumvoltages through the wire mesh embedded in an electrostatic chuck of theplasma reactor. By combining the high voltage pulsed DC source, and thesecond voltage source for low and medium voltages, the ion energydistributions are controllable by shifting the high voltage pulsed DCsource to create a group of ions with energy in the range from 1,000 to10,000 eV, while the lower ion energies can be tuned to form peaks oreven bands of ion energies in the range of 0 to 1,500 eV. Accordingly,the ion energy distribution is tailored in the low and high energyranges to give a desired ion energy distribution.

FIG. 1 is a block diagram illustrating a system 100 for tunableworkpiece biasing in accordance with exemplary embodiments of thepresent disclosure.

In various embodiments, the system 100 of FIG. 1 can comprise componentsof a plasma processing chamber such as the AVATAR®, ADVANTEDGE™ MESA™,SYM3®, DPS®, PRECISION®, and PRODUCER®™ process chambers available fromApplied Materials, Inc. of Santa Clara, Calif. or other processchambers.

The system 100 comprises a plasma chamber 102, an electrostatic chuck104, a cooling base 106, a chucking mesh 108, a pulsed DC source 120 (orpulsing source), a shaped bias waveform generator 130, a biasingcontroller 140, an edge ring 150 and an anode 160. According toexemplary embodiments, the chucking mesh 108 is embedded in theelectrostatic chuck 104. The electrostatic chuck 104 supports theworkpiece, while the cooling base 106 supports the electrostatic chuck104. The plasma chamber 102 further comprises a plurality of pins 122that are disposed on the cooling base 106 at one end and extend throughthe electrostatic chuck 104 to make contact with the wafer 105 at theother end.

The plasma chamber 102 performs various operations and processes on aworkpiece, such as wafer 105, by exposing the wafer 105 to plasma 101.The wafer 105 is placed inside the plasma chamber 102 and reactant gasesare introduced into the chamber, the gases being irradiated withelectromagnetic energy to ignite and maintain the plasma 101.

Depending upon the composition of the gases from which the plasma 101 isformed, the plasma 101 may be employed to etch a particular thin filmfrom the wafer 105 or may be employed to deposit a thin film layer ontothe wafer 105. The plasma 101 generally has a high ion density so that ahigh etch or deposition rate can be achieved on the wafer, and also sothat less time is required to perform a given etch or depositionprocess, thus increasing throughput.

Independent control of the pulsed DC source 120 and the shaped biaswaveform generator 130 is maintained by the biasing controller 140. Insome embodiments, the biasing controller 140 is independent computersystem which receives and sets parameters for the pulsed DC source 120and the shaped bias waveform generator 130.

Pulsed DC sources previously have been used in applications forprocessing a wafer such as ion implantation. For some applications suchas shallow junction formation in semiconductors, plasma doping systemsare used. In a plasma doping system, a semiconductor wafer is placed ona conductive platen which functions as a cathode. An ionizable gascontaining the desired dopant material is introduced into the chamber,and a high voltage pulse is applied between the platen and an anode orthe chamber walls, establishing a plasma sheath in the vicinity of thewafer. The applied voltage causes ions in the plasma to cross the plasmasheath and to be implanted into the wafer. In plasma doping systems, thehigh voltage pulse from a pulsed DC source accelerates positive ionsfrom the plasma towards the wafer, and in plasma doping applications thedepth of implantation is related to the voltage applied between thewafer and the anode (or chamber wall). A plasma doping system using apulsed DC source is described further in U.S. Pat. Nos. 5,354,381 and6,020,592.

The pulsed DC source 120 couples high voltage directly to a workpiece,such as wafer 105, via pins 122 and the anode 160 (or alternatively, thechamber walls). In embodiments, the pulsed DC source 120 generates highvoltage pulses in the form of a cyclic waveform, for example, thewaveform 600 illustrated in FIG. 6, where one cycle of the waveformcomprises a first portion where the voltage is non-zero and a secondportion where the voltage is zero. In exemplary embodiments, thenon-zero voltage during the first portion is in the range fromapproximately 1 to 10 kV. In embodiments, the first portion is between5% and 95% of the duration of a cycle; often expressed as the duty cycleof the cyclic waveform is between 5% and 95%. In embodiments, the pulsefrequency of the cyclic waveform is between 100 Hz and 100,000 Hz.

In embodiments, the first portion of the waveform 600 comprises a firstnon-zero voltage and a second non-zero voltage. In embodiments, thefirst non-zero voltage and the second non-zero voltage are sequential intime. In embodiments, a non-zero voltage can be one or more than onevalue in successive pulses. In embodiments, a non-zero voltage can beone value for a first number of cycles, and a second value for a secondnumber of cycles. In embodiments, the first number of cycles and thesecond number of cycles are repeated.

According to another embodiment shown in FIG. 7, direct contact with apulsed DC source to the workpiece is made through pins 122, but each pinis electrically isolated from the base and electrically isolated fromeach other pin. Each of the pins 122 is individually connected to anindependent pulsed DC source, e.g., pulsed DC source 702-1, 702-2, 702-3and 702-4 (collectively, pulsed DC source 702). In yet anotherembodiment illustrated in FIG. 8, a first group of pins 804 which areelectrically isolated from the base is connected to a first pulsed DCsource 802-1, and a second group of pins 806 which are electricallyisolated from the base is connected to a second pulsed DC source 802-2(collectively, pulsed DC source 802), such that the first and secondgroups of pins do not have any common members. Generally, coupling pinsto independent pulsed DC sources allows local spatial control of the ionenergy distribution across a workpiece, which allows for adjustment forother non-uniformities in the processing system. Also, the system can beadjusted for non-uniformities that exist on the wafer from priorprocesses, or to adjust for expected non-uniformities in subsequentprocesses. In such embodiments, independently controlling the pulsed DCsources to each pin compensates for edge effects at the edge of thewafer.

In the embodiments described in FIG. 7 and FIG. 8, the shaped biaswaveform generator 130 is optional and the pulsed DC sources 702 and 802provide tailored ion distributions by controlling the voltages acrosseach source by the biasing controller 140. The shaped bias waveformgenerator 130 can be included to enhance the tailoring of the iondistribution across the workpiece, or for ion implantation inspecialized features of the workpiece.

The shaped bias waveform generator 130 is directly coupled to thechucking mesh 108, though in some embodiments, the shaped bias waveformgenerator 130 may be coupled to power electrode 113. By applying thewaveform bias (for example, shown in FIG. 6) to the chucking mesh 108,the voltage drop across the chuck capacitance is so small that thevoltage amplitude measurable at the workpiece (e.g., wafer 105) surface,at any time during the application of the bias pulse substantiallyapproximates the voltage amplitude of the pulse (i.e., does not varymore than 0 to 5%).

The chucking mesh 108 is capacitively coupled to the wafer 105. Theshaped bias waveform generator 130 supplies pulsed voltages in theexemplary range of 0 to 1.5 kV (e.g., low to medium voltages). In someembodiments, the shaped bias waveform generator 130 provides a constantor continuous voltage to the wafer 105 via the chucking mesh 108, whilein other embodiments the shaped bias waveform generator 130 isconfigured to provide voltage ramps, allowing for broadband ion energydistribution. In a broadband ion energy distribution, ions obtainenergies in a continuous range from a first ion energy to a second ionenergy, where the second ion energy is larger than the first ion energy.In embodiments, the first ion energy is defined as the energy which isless than the energy of 95% of the ions accelerated due to coupling ofshaped bias waveform generator 130. In some embodiments, the second ionenergy is defined as the energy which is greater than the energy of 95%of the ions accelerated due to coupling of shaped bias waveformgenerator 130. According to one embodiment, the first ion energy is 10eV and the second ion energy is 3000 eV.

In an embodiment, the high voltage cyclic waveform from the pulsed DCsource 120 can vary from 100 Hz and 100,000 Hz in range, while theshaped bias waveform generator 130 pulses at 400 kHz according to someembodiments. In some embodiments, the pulses emitted from the shapedbias waveform generator 130 occur during the second portion of the DCpulsing cycle when the DC voltage from the pulsed DC source 120 is zero.

The biasing controller 140 controls the ion energy distributions bysetting a non-zero voltage from the pulsed DC source 120 during thefirst portion of the DC pulsing cycle anywhere from 1 kV to 10 kV, whilethe lower and medium ion energies can be tuned to form peaks or bands ofenergy in the range of 0 kV to 1.5 kV. Thus, the ion energy distributioncan be tailored in the low, medium, and high energy ranges to give adesired distribution. Such ion energy distribution control isadvantageous, for example, in embodiments where ions are required toreach the bottom of high aspect ratio features in wafer 105. One suchapplication is the 3D-NAND memory hole etch, where aspect ratios areroutinely greater than 30:1.

During the second portion of the pulsed DC cycle, the biasing controller140 evaluates a received voltage from the wafer 105 via, for example, avoltage probe (or some other equivalent implement) and, if the voltagehas changed from previous readings and/or is not within a tolerance of apredetermined voltage level, the biasing controller 140 determines acontrol signal to be communicated to the shaped bias waveform generator130 to adjust the voltage being provided by the shaped bias waveformgenerator 130 to the chucking mesh 108 to cause the voltage at the wafer105 to remain constant and/or within a tolerance of a predeterminedvoltage level.

In one embodiment, the biasing controller 140 implements an iterativeprocess to determine a control signal to communicate to the shaped biaswaveform generator 130. For example, in one embodiment, upon determiningthat the voltage received requires adjustment, the biasing controller140 communicates a signal to the shaped bias waveform generator 130 tocause an adjustment in the voltage being supplied by the shaped biaswaveform generator 130 to the chucking mesh 108. After the adjustment,the voltage at the wafer 105 is again evaluated by the biasingcontroller 140. If the voltage captured at the wafer 105 has become moreconstant or closer to the tolerance of the predetermined voltage level,but still requires more adjustment, the biasing controller 140communicates another control signal to the shaped bias waveformgenerator 130 to cause an adjustment to the voltage being supplied bythe shaped bias waveform generator 130 to the chucking mesh 108 in thesame direction. If, after adjustment, the voltage captured at thesubstrate has become less constant or farther from the predeterminedvoltage level, the biasing controller 140 communicates another controlsignal to the shaped bias waveform generator 130 to cause an adjustmentto the voltage being supplied by the shaped bias waveform generator 130to the chucking mesh 108 in the opposite direction. Such adjustments cancontinue to be made until the voltage at the substrate remains constantand/or within a tolerance of a predetermined voltage level. In oneembodiment, the biasing controller 140 digitizes the voltage signal froma reading from the wafer 105 and communicates the digitized voltagesignal to the bias supply to periodically adjust the shaped pulse biaswaveform so that the wafer (substrate) voltage remains constant and/orwithin a tolerance of a predetermined voltage level.

In other embodiments in accordance with the present principles, a signalrepresentative of the voltage at a workpiece being processed (e.g.,wafer 105) can be captured using the optional edge ring 150. Forexample, in one embodiment and with reference back to FIG. 3, the edgering 150 is used to sense voltage measurements representative of avoltage at a substrate being processed. In one embodiment in accordancewith the present principles, the edge ring 150 is located directly belowthe chucking mesh 108 and is large enough to overlap the edges of anypower electrode to which the shaped bias waveform generator 130 may becoupled, according to an embodiment where the shaped bias waveformgenerator 130 is coupled directly to a power electrode instead of thechucking mesh 108. Because of the composition and location of the edgering 150, the edge ring 150 is electrically coupled to the workpiecebeing processed so as to sense a voltage at the workpiece beingprocessed which is within, for example, 5 to 7 percent of the actualvoltage at the workpiece.

The low and medium energy ions from the shaped bias waveform generator130 complement the high energy peak from the pulsed DC source 120 andstimulate other beneficial properties. For example, the low and mediumenergy ions aid polymer sidewall deposition, resulting in reduced bow indeep etches and improved mask selectivities.

FIG. 2 is a block diagram of the biasing controller 140 in accordancewith exemplary embodiments of the present disclosure.

Various embodiments of method and apparatus for tailoring iondistribution may be executed by the biasing controller 140. According toone embodiment, the biasing controller 140 comprises one or more CPUs 1to N, support circuits 204, I/O circuits 206 and system memory 208. Thesystem memory 208 may further comprise tuning parameters 210 and abiasing program 220. The CPUs 1 to N are operative to execute one ormore applications which reside in system memory 208. The biasingcontroller 140 may be used to implement any other system, device,element, functionality or method of the above-described embodiments. Inthe illustrated embodiments, the biasing controller 140 may beconfigured to implement method 400 (FIG. 4) as processor-executableexecutable program instructions. The biasing program 220 controls theoperation of both the pulsed DC source 120 and the shaped bias waveformgenerator 130 for tailored ion distribution across wafer 105.

In different embodiments, biasing controller 140 may be any of varioustypes of devices, including, but not limited to, a personal computersystem, desktop computer, laptop, notebook, or netbook computer,mainframe computer system, handheld computer, workstation, networkcomputer, a mobile device such as a smart phone or PDA, a consumerdevice, or in general any type of computing or electronic device.

In various embodiments, biasing controller 140 may be a uniprocessorsystem including one processor, or a multiprocessor system includingseveral processors (e.g., two, four, eight, or another suitable number).CPUs 1 to N may be any suitable processor capable of executinginstructions. For example, in various embodiments, CPUs 1 to N may begeneral-purpose or embedded processors implementing any of a variety ofinstruction set architectures (ISAs). In multiprocessor systems, each ofCPUs 1 to N may commonly, but not necessarily, implement the same ISA.

System memory 208 may be configured to store program instructions and/ordata accessible by CPUs 1 to N. In various embodiments, system memory208 may be implemented using any suitable memory technology, such asstatic random access memory (SRAM), synchronous dynamic RAM (SDRAM),nonvolatile/Flash-type memory, or any other type of memory. In theillustrated embodiment, program instructions and data implementing anyof the elements of the embodiments described above may be stored withinsystem memory 208. In other embodiments, program instructions and/ordata may be received, sent or stored upon different types ofcomputer-accessible media or on similar media separate from systemmemory 208 or biasing controller 140.

In one embodiment, I/O circuits 206 may be configured to coordinate I/Otraffic between CPUs 1 to N, system memory 208, and any peripheraldevices in the device, including a network interface or other peripheralinterfaces, such as input/output devices. In some embodiments, I/Ocircuits 206 may perform any necessary protocol, timing or other datatransformations to convert data signals from one component (e.g., systemmemory 208) into a format suitable for use by another component (e.g.,CPUs 1 to N). In some embodiments, I/O circuits 206 may include supportfor devices attached through various types of peripheral buses, such asa variant of the Peripheral Component Interconnect (PCI) bus standard orthe Universal Serial Bus (USB) standard, for example. In someembodiments, the function of I/O circuits 206 may be split into two ormore separate components, such as a north bridge and a south bridge, forexample. Also, in some embodiments some or all of the functionality ofI/O circuits 206, such as an interface to system memory 208, may beincorporated directly into CPUs 1 to N.

A network interface may be configured to allow data to be exchangedbetween biasing controller 140 and other devices attached to a network,such as one or more display devices (not shown), or one or more externalsystems or between nodes. In various embodiments, a network may includeone or more networks including but not limited to Local Area Networks(LANs) (e.g., an Ethernet or corporate network), Wide Area Networks(WANs) (e.g., the Internet), wireless data networks, some otherelectronic data network, or some combination thereof. In variousembodiments, the network interface may support communication via wiredor wireless general data networks, such as any suitable type of Ethernetnetwork, for example; via telecommunications/telephony networks such asanalog voice networks or digital fiber communications networks; viastorage area networks such as Fiber Channel SANs, or via any othersuitable type of network and/or protocol.

Input/output devices may, in some embodiments, include one or moredisplay terminals, keyboards, keypads, touchpads, scanning devices,voice or optical recognition devices, or any other devices suitable forentering or accessing data by one or more biasing controller 140.Multiple input/output devices may be present or may be distributed onvarious nodes of biasing controller 140. In some embodiments, similarinput/output devices may be separate from biasing controller 140 and mayinteract with one or more nodes of biasing controller 140 through awired or wireless connection, such as over a network interface.

In some embodiments, the illustrated computer system may implement anyof the methods described above, such as the methods illustrated by theflowcharts of FIG. 4. In other embodiments, different elements and datamay be included.

Those skilled in the art will appreciate that biasing controller 140 ismerely illustrative and is not intended to limit the scope ofembodiments. In particular, the computer system and devices may includeany combination of hardware or software that can perform the indicatedfunctions of various embodiments, including computers, network devices,Internet appliances, PDAs, wireless phones, pagers, and the like.Biasing controller 140 may also be connected to other devices that arenot illustrated, or instead may operate as a stand-alone system. Inaddition, the functionality provided by the illustrated components mayin some embodiments be combined in fewer components or distributed inadditional components. Similarly, in some embodiments, the functionalityof some of the illustrated components may not be provided and/or otheradditional functionality may be available.

Those skilled in the art will also appreciate that, while various itemsare illustrated as being stored in memory or on storage while beingused, these items or portions of them may be transferred between memoryand other storage devices for purposes of memory management and dataintegrity. Alternatively, in other embodiments some or all of thesoftware components may execute in memory on another device andcommunicate with the illustrated computer system via inter-computercommunication. Some or all of the system components or data structuresmay also be stored (e.g., as instructions or structured data) on acomputer-accessible medium or a portable article to be read by anappropriate drive, various examples of which are described above. Insome embodiments, instructions stored on a computer-accessible mediumseparate from biasing controller 140 may be transmitted to biasingcontroller 140 via transmission media or signals such as electrical,electromagnetic, or digital signals, conveyed via a communication mediumsuch as a network and/or a wireless link. Various embodiments mayfurther include receiving, sending or storing instructions and/or dataimplemented in accordance with the foregoing description upon acomputer-accessible medium or via a communication medium. In general, acomputer-accessible medium may include a storage medium or memory mediumsuch as magnetic or optical media, e.g., disk or DVD/CD-ROM, volatile ornon-volatile media such as RAM (e.g., SDRAM, DDR, RDRAM, SRAM, and thelike), ROM, and the like.

FIG. 3 is one example of an ion energy distribution function as shown ingraph 300 of the apparatus of FIG. 1, in accordance with exemplaryembodiments of the present disclosure.

The graph 300 illustrates a first curve 302 and a second curve 304. Thefirst curve 302 illustrates the distribution of ions at differing lowand medium ion energies, caused by the shaped bias waveform generator130. The second curve 304 illustrates the ion distribution at high ionenergies, showing a high energy peak from the pulsed DC source 120.While the distribution from the shaped bias waveform generator discussedabove is roughly square, other distributions are possible with thetunable biasing described in the present disclosure because the shapedbias waveform generator is independently controlled from the high ionenergy peak which comes from the pulsed DC source 120.

For example, the low end of first curve 302 may be disposed towardslower ion energies, for example, approximately 100 V, while the mediumend is disposed towards higher ion energies, for example approximately800 V. In an additional embodiment, the low end of first curve 302 maybe disposed towards lower ion energies, for example, approximately 200V, while the medium end is disposed towards higher ion energies, forexample approximately 1000 V. In yet another embodiment, the low end offirst curve 302 may be disposed towards lower ion energies, for example,approximately 20 V, while the medium end is disposed towards higher ionenergies, for example approximately 500 V.

FIG. 4 is a flow diagram representing a method 400 of tailoring the iondistribution across a semiconductor workpiece in a plasma chamber inaccordance with exemplary embodiments of the present disclosure.

The biasing controller 140 is an exemplary implementation of the method400 in accordance with exemplary embodiments of the present disclosure.

At 402, the biasing controller begins method 400. At 404, the biasingcontroller controls the pulsed DC source 120 to generate a high voltage,and to couple the high voltage to a wafer in a plasma chamber, e.g.,wafer 105 in plasma chamber 102.

At 406, the biasing controller controls the shaped bias waveformgenerator 130 to generate low and medium voltages. At 408, these low andmedium voltages are coupled, capacitively, to a wafer.

The method then proceeds to 410, where the biasing controller 140alternatively pulses the high voltage and the medium and low voltages,to tailor ion energy distribution of the flux of ions directed towardsthe workpiece, such that high energy ions are available to reach thebottom of high aspect ratio features in the workpiece.

The method 400 ends at 412.

FIG. 5 illustrates a shaped pulse bias waveform emitted by the shapedbias waveform generator 130, and coupled to a plasma chamber inaccordance with exemplary embodiments of the present disclosure.

The shaped bias waveform generator 130 couples the pulsed waveform shownin FIG. 5 to the chucking mesh 108 of the system 100.

For the shaped pulse bias to function as intended, currently severalcapacitance values must be either known or estimated. In particular, theshaped pulse bias waveform (FIG. 5) requires that the total voltagesupplied to the chucking mesh 108 is divided among the electrostaticchuck 104 and the sheath charge which forms in the space between theplasma and the electrostatic chuck support surface or workpiece disposedthereon (referred to as the “space charge sheath” or “sheath”). While anelectrostatic chuck capacitance, C_(CK), can be readily ascertained,values of stray capacitance (C_(STR)) and sheath capacitance (C_(SH))have been found to vary unpredictably with respect to time. The straycapacitance, C_(STR), for example, is determined by conditions within aplasma processing chamber and, accordingly, is sensitive to such factorsas thermal expansion of processing chamber components and the like.

Functionally, the electrostatic chuck and sheath act as two capacitorsconnected in series, and since the input voltage waveform applied to oneof the electrodes of the electrostatic chuck capacitor is controlled, todetermine how the total applied voltage will split between thecapacitors and how much voltage there will be on the sheath, bothcapacitance values need to be known.

The methods described herein may be implemented in software, hardware,or a combination thereof, in different embodiments. In addition, theorder of methods may be changed, and various elements may be added,reordered, combined, omitted or otherwise modified. All examplesdescribed herein are presented in a non-limiting manner. Variousmodifications and changes may be made as would be obvious to a personskilled in the art having benefit of the present disclosure.Realizations in accordance with embodiments have been described in thecontext of particular embodiments. These embodiments are meant to beillustrative and not limiting. Many variations, modifications,additions, and improvements are possible within the scope of the presentdisclosure. Accordingly, plural instances may be provided for componentsdescribed herein as a single instance. Finally, structures andfunctionality presented as discrete components in the exampleconfigurations may be implemented as a combined structure or component.These and other variations, modifications, additions, and improvementsmay fall within the scope of embodiments as defined in the claims thatfollow.

While the foregoing is directed to embodiments of the presentdisclosure, other and further embodiments of the disclosure may bedevised without departing from the basic scope thereof.

The invention claimed is:
 1. A system for tunable workpiece biasing,comprising: a plasma chamber that performs plasma processing on aworkpiece; a first pulsed voltage source using DC voltages, coupleddirectly to the workpiece in the plasma chamber via at least one directconnection, the at least one direct connection enabling ion energycontrol in the workpiece near the at least one direct connection; asecond pulsed voltage source, coupled capacitively to the workpiece; anda biasing controller comprising one or more processors, and memory,wherein the memory comprises a set of computer instructions that whenexecuted by the one or more processors, the biasing controller isconfigured to independently control the first pulsed voltage source andthe second pulsed voltage source based on one or more voltage parametersof the first pulsed voltage source and the second pulsed voltage sourcein order to tailor ion energy distribution of the flux of ions directedto the workpiece, the biasing controller is configured to adjust thefirst and second pulsed voltage sources in combination to achieve aconfigurable ion energy distribution in the workpiece.
 2. The system ofclaim 1, wherein the second pulsed voltage source outputs a shaped biaswaveform.
 3. The system of claim 1, wherein the biasing controlleralternatively pulses the first pulsed voltage source and the secondpulsed voltage source.
 4. The system of claim 1, wherein the firstpulsed voltage source supplies a first pulse at high voltage, whereinthe maximum of the high voltage during a first pulse is approximately inthe range of 1 to 10 kV.
 5. A system for tunable workpiece biasing,comprising: a plasma chamber that performs plasma processing on aworkpiece: a first pulsed voltage source using DC voltages, coupleddirectly to the workpiece in the plasma chamber via at least one directconnection, the at least one direct connection enabling ion energycontrol in the workpiece near the at least one direct connection; asecond pulsed voltage source, coupled capacitively to the workpiece; anda biasing controller comprising one or more processors, and memory,wherein the memory comprises a set of computer instructions that whenexecuted by the one or more processors, the biasing controller isconfigured to independently control the first pulsed voltage source andthe second pulsed voltage source based on one or more voltage parametersof the first pulsed voltage source and the second pulsed voltage sourcein order to tailor ion energy distribution of the flux of ions directedto the workpiece, wherein the first pulsed voltage source supplies afirst pulse at high voltage, wherein the maximum of the high voltageduring a first pulse is approximately in the range of 1 to 10 kV andwherein the second pulsed voltage source supplies a second pulsecomprising one or more voltages in a continuous range of low to mediumvoltages, wherein the range is greater than 0 to approximately 1.5 kV.6. The system of claim 1, wherein the plasma chamber further comprises:an electrostatic chuck supporting the workpiece; a base supporting theelectrostatic chuck; a plurality of pins, each directly coupled to thebase at one end, and configured to be directly coupled to the workpieceat the other end; and a chucking mesh embedded within the electrostaticchuck.
 7. The system of claim 6, wherein the first pulsed voltage sourceis coupled to the base, and voltage supplied from the first pulsedvoltage source is directly coupled to the workpiece via the plurality ofpins.
 8. The system of claim 7, wherein the second pulsed voltage sourceis coupled directly to the chucking mesh, and the chucking mesh isconfigured to be capacitively coupled to the workpiece.
 9. The system ofclaim 8, wherein the biasing controller is configured to adjust the oneor more voltage parameters to modify a waveform emitted by the secondpulsed voltage source, based on voltages sensed at the workpiece. 10.The system of claim 1, wherein the first pulsed voltage source emitshigh voltage pulses at a pulse frequency of approximately 100 to 100,000Hz.
 11. The system of claim 10, wherein the second pulsed voltage sourceemits pulses at a pulse frequency of approximately 400 kHz.
 12. A methodfor tunable workpiece biasing in a plasma chamber comprising: generatinga high voltage by a first pulsed voltage source using DC voltages andcoupling the high voltage to a workpiece in a plasma chamber via atleast one direct connection, the at least one direct connection enablingion energy control in the workpiece near the at least one directconnection; generating one or more of low and medium voltages by asecond pulsed voltage source; coupling, capacitively, the one or more oflow and medium voltages to the workpiece; and pulsing the high voltageand the one or more of low and medium voltages by a biasing controlleraccording to, one or more voltage parameters of the first pulsed voltagesource and the second pulsed voltage source to tailor ion distributionin the workpiece, the biasing controller adjusting the first and secondpulsed voltage sources in combination to achieve a configurable ionenergy distribution in the workpiece.
 13. The method of claim 12,wherein the biasing controller accepts a bias waveform as input for thesecond pulsed voltage source.
 14. A method for tunable workpiece biasingin a plasma chamber comprising: generating a high voltage by a firstpulsed voltage source and coupling the high voltage to a workpiece in aplasma chamber; generating one or more of low and medium voltages by asecond pulsed voltage source; coupling, capacitively, the one or more oflow and medium voltages to the workpiece; and pulsing the high voltageand the one or more of low and medium voltages by a biasing controlleraccording to, one or more voltage parameters of the first pulsed voltagesource and the second pulsed voltage source to tailor ion distributionin the workpiece; wherein the first pulsed voltage source supplies ahigh voltage, the maximum of the high voltage during a pulse beingapproximately 1 to 10 kV, and wherein the second pulsed voltage sourcesupplies one or more voltages in a continuous range of low to mediumvoltages, wherein the range is greater than 0 to approximately 1.5 kV.15. The method of claim 14, wherein the first pulsed voltage sourceemits high voltage pulses at a pulse frequency of approximately 100 to100,000 Hz, and the second pulsed voltage source emits pulses at a pulsefrequency of approximately 400 kHz.
 16. The method of claim 12, whereinthe plasma chamber further comprises: an electrostatic chuck supportingthe workpiece; a base supporting the electrostatic chuck; a plurality ofpins, each directly coupled to the base at one end, and directly coupledto the workpiece at the other end; and a chucking mesh embedded withinthe electrostatic chuck.
 17. The method of claim 16, wherein the firstpulsed voltage source is coupled to the base, and voltage supplied fromthe first pulsed voltage source is directly coupled to the workpiece viathe plurality of pins, and wherein the second pulsed voltage source iscoupled directly to the chucking mesh, and the chucking mesh iscapacitively coupled to the workpiece.
 18. The method of claim 17wherein the biasing controller adjusts the one or more voltageparameters to modify a waveform emitted by the second pulsed voltagesource, based on voltages sensed at the workpiece.